1. Field of the Invention
The present invention relates to an image forming apparatus, and more particularly, to an image forming apparatus in which an image forming unit is mounted on a carriage to reciprocate the image forming unit.
2. Description of the Related Art
As an image forming apparatus for such devices as a printer, a facsimile machine, a copier, a plotter, and a multifunction peripheral (MFP) of such devices, as an image forming apparatus, an ink-jet recording apparatus or the like is known as a liquid discharge recording type image forming apparatus using, for example, a recording head for discharging ink droplets. This liquid discharge recording type image forming apparatus forms (records, prints out, or reproduces are used as synonyms) an image by discharging ink droplets from the recording head onto a sheet being conveyed (a sheet is not limited to a paper sheet, but includes an OHP sheet and the like; a sheet means something to which ink droplets or other liquids adhere; a sheet is also referred to as a medium to be recorded, a recording medium, recording paper, a recording sheet, etc.), and includes a serial-type image forming apparatus and a line-type image forming apparatus using a line-type head. The serial-type image forming apparatus forms an image by discharging droplets from the recording head while moving the recording head in a main scanning direction. The line-type image forming apparatus forms an image by discharging droplets from the recording head in a state where the recording head is not moved.
Incidentally, in the present application, a liquid discharge recording type “image forming apparatus” means an apparatus that forms an image by discharging a liquid onto a medium, such as paper, yarn, fiber, fabric, leather, metal, plastic, glass, wood, and ceramic. Furthermore, to “form an image” means not only to provide an image having a meaning, such as a text and a drawing, on the medium but also to provide an image having no meaning, such as a pattern, on the medium (just make droplets land on the medium). Moreover, “ink” is not limited to a material referred to as ink, but includes anything that can be turned into a liquid when discharged, such as a DNA sample, resist, and a pattern material. Furthermore, an “image” is not limited to a planar image, but includes an image formed on a sterically-formed medium and an image formed by three-dimensionally modeling a solid body.
As such an image forming apparatus, as described above, there is known a serial-type image forming apparatus in which a recording head including a liquid discharge head, which is an image forming unit, is mounted on a carriage. The serial-type image forming apparatus forms an image by discharging droplets from the recording head while moving the liquid discharge head in a main scanning direction and intermittently moving a medium in a sub-scanning direction perpendicular to the main scanning direction. Incidentally, in the following, an example where the image forming unit is a liquid discharge head is described; however, the image forming unit is not limited to the liquid discharge head, and the present invention may be equally applied to other image forming units.
In such a serial-type image forming apparatus, the reciprocating movement of the carriage mounting thereon the recording head triggers vibration of the main body of the apparatus. Especially, with an increase in the moving speed of the carriage to achieve an increase in the speed of a print job, the acceleration and deceleration of the carriage during the main scanning become more rapid, and thus the vibration of the main body of the apparatus becomes larger. Furthermore, in an MFP equipped with an image reading device (a scanner), due to the vibration of the main body of the apparatus occurring at the side of the image forming unit, the scanner when reading an image is vibrated, which causes a degradation of the read image.
Therefore, conventionally, vibration of the carriages is dampened. For example, as disclosed in Japanese Patent Application Laid-open No. 2001-138499 and Japanese Patent Application Laid-open No. 2005-081673, it is known that a vibration damping member having about the same mass as a carriage is attached to a timing belt for moving the carriage. The vibration of the carriage is dampened by moving the carriage and the vibration damping member in opposite directions to each other.
Furthermore, an apparatus is disclosed in Japanese Patent Application Laid-open No. H3-256772. The apparatus includes a weight having about the same mass as a printer head and a scanning mechanism for moving the weight in the opposite direction to the moving direction of the printer head at the same acceleration as the printer head. This scanning mechanism for moving the weight is separate from the scanning mechanism for moving the carriage.
Moreover, as disclosed in Japanese Patent Application Laid-open No. 2005-212160, it is known that impact force applied on a main body of a printer is detected and a supporting power of a printer supporting unit is controlled in accordance with the detected impact force. In addition, an apparatus is disclosed in Japanese Patent Application Laid-open No. 2003-237165, which includes a vibration damping unit for dampening the vibration of a transmitting member for transmitting a driving force to a carriage.
However, as in the conventional technologies such as Japanese Patent Application Laid-open No. 2001-138499 and Japanese Patent Application Laid-open No. 2005-081673, if a vibration damping member (also referred to as a “counter weight”) is attached to a timing belt for moving a carriage, the counter weight also moves (for dampening vibration of the carriage) every time the carriage moves; therefore, if there is a minute variation in the moving speed of the carriage, if there is a variation in the moving load on the carriage, or if there is a variation in the weight of the carriage due to a change in the remaining amount of ink if an apparatus includes an ink tank, and the like, the damping action of the vibration damping member produces vibration of the carriage rather than counteracts the vibration of the carriage. This means that, for example, when a liquid discharge head is used, the accuracy of the droplet landing position is decreased, and thus the image quality may be degraded.
In addition, there are problems in that the load on a drive source of a main scanning mechanism for moving the carriage increases, and in that the weight and size of the entire apparatus increase because of the use of the vibration damping member having about the same mass as the carriage.
Consequently, as disclosed in Japanese Patent Application Laid-open No. H3-256772, by employing a separate drive source for moving the vibration damping member from the drive source for moving the carriage, the problems associated with the vibration damping mechanism using the same drive source as the carriage may be resolved.
However, in such a configuration, the carriage and the vibration damping member, which are driven by the different drive sources, have to be moved in the opposite directions by the same forces and at the same timings; therefore, there arises a problem that a configuration for controlling the forces and timings to be synchronized with each other has to be designed without complicating the configuration and applying high load to a control device.